Only one-tenth of a single percent of DNA (about 3 million bases) differs from one person to the next. Scientists can use these differant parts to generate a DNA profile of an individual, using samples from blood, bone, hair, and other body tissues and products.
In criminal cases, this generally involves obtaining samples from crime-scene evidence and a suspect, extracting the DNA, and analyzing it for the presence of a set of specific DNA parts (markers).
If the sample profiles don't match, the person did not contribute the DNA at the crime scene.
If the patterns match, the suspect may have contributed the evidence sample. How does forensic identification work?
Any type of organism can be identified by examination of DNA sequences unique to that species. Identifying individuals within a species is not as accurate at this time, although when DNA sequencing technologies get better, direct comparison of very large DNA segments, and possibly even whole genomes, will become possible and will allow precise individual identification.
To identify individuals, forensic scientists scan 13 DNA parts, or loci, that vary from person to person and use the data to create a DNA profile of that individual (sometimes called a DNA fingerprint). There is an extremely small chance that another person has the same DNA profile for a particular set of 13 pieces. Some Examples of DNA Uses for Forensic Identification
Identify suspects whose DNA may match evidence left at crime scenes
Exonerate persons wrongly accused of crime
Identify crime and catastrophe victims
Detect bacteria and other organisms that may pollute air, water, soil, and food
http://www.ornl.gov/sci/techresources/Human_Genome/elsi/forensics.shtml Types of DNA testing
Two different DNA tests exist, the RFLP and the PCR. Both are very accurate, but they’re performed in different ways.The restriction fragment length polymorphism or RFLP called DNA fingerprinting or profiling is considered to be the more accurate of the two. This test examines sequences of base pairs in a section of a DNA strand with a high probability of being completely unique to the donor. When a match is found, there is no question that the donor was at the scene of the crime. It’s very conclusive and finalizing. Unfortunately, the RFLP requires many sample cells from the crime scene like several strands of hair or large splatters of blood. The cells have to be undamaged and recently dead. The test takes anywhere from 3 weeks to three months to complete. Although the PCR test, or polymerase chain reaction test, isn’t quite as accurate, it takes a week at mostto complete. The test can be performed with minute crime scene samples, to, which helps investigators who have little physical evidence. The DNA doesn’t have to be recently collected, either; the PCR test can still be performed even decades after the cells have died, and still be just as accurate. This is because the PCT method involves copying the available DNA and analyzing only one specific gene, oftentimes the gene called HLA DQ alpha. Geneticists look for certain types of the gene (alleles) to determine matches. If no match is found, the donor was not at the crime scene. http://library.thinkquest.org/28599/application.shtml
Basics of DNA Typing
Only one-tenth of a single percent of DNA (about 3 million bases) differs from one person to the next. Scientists can use these differant parts to generate a DNA profile of an individual, using samples from blood, bone, hair, and other body tissues and products.In criminal cases, this generally involves obtaining samples from crime-scene evidence and a suspect, extracting the DNA, and analyzing it for the presence of a set of specific DNA parts (markers).
If the sample profiles don't match, the person did not contribute the DNA at the crime scene.
If the patterns match, the suspect may have contributed the evidence sample.
How does forensic identification work?
Any type of organism can be identified by examination of DNA sequences unique to that species. Identifying individuals within a species is not as accurate at this time, although when DNA sequencing technologies get better, direct comparison of very large DNA segments, and possibly even whole genomes, will become possible and will allow precise individual identification.
To identify individuals, forensic scientists scan 13 DNA parts, or loci, that vary from person to person and use the data to create a DNA profile of that individual (sometimes called a DNA fingerprint). There is an extremely small chance that another person has the same DNA profile for a particular set of 13 pieces.
Some Examples of DNA Uses for Forensic Identification
- Identify suspects whose DNA may match evidence left at crime scenes
- Exonerate persons wrongly accused of crime
- Identify crime and catastrophe victims
- Detect bacteria and other organisms that may pollute air, water, soil, and food
http://www.ornl.gov/sci/techresources/Human_Genome/elsi/forensics.shtmlTypes of DNA testing
Two different DNA tests exist, the RFLP and the PCR. Both are very accurate, but they’re performed in different ways.The restriction fragment length polymorphism or RFLP called DNA fingerprinting or profiling is considered to be the more accurate of the two. This test examines sequences of base pairs in a section of a DNA strand with a high probability of being completely unique to the donor. When a match is found, there is no question that the donor was at the scene of the crime. It’s very conclusive and finalizing. Unfortunately, the RFLP requires many sample cells from the crime scene like several strands of hair or large splatters of blood. The cells have to be undamaged and recently dead. The test takes anywhere from 3 weeks to three months to complete. Although the PCR test, or polymerase chain reaction test, isn’t quite as accurate, it takes a week at mostto complete. The test can be performed with minute crime scene samples, to, which helps investigators who have little physical evidence. The DNA doesn’t have to be recently collected, either; the PCR test can still be performed even decades after the cells have died, and still be just as accurate. This is because the PCT method involves copying the available DNA and analyzing only one specific gene, oftentimes the gene called HLA DQ alpha. Geneticists look for certain types of the gene (alleles) to determine matches. If no match is found, the donor was not at the crime scene.
http://library.thinkquest.org/28599/application.shtml